Thermodynamic cycle heat engines (hereinafter referred to as engines or heat engines) apply the principles of heat regeneration and thermodynamic cycles to provide the power for the engine. These engines can be adapted to implement a number of thermodynamic cycles including the Stirling cycle. An engine employing the Stirling cycle (hereinafter referred to as a Stirling engine) includes a high temperature or expansion chamber and a low temperature or compression chamber. To increase efficiency, a regenerator also is added. Thermodynamic heat engines can typically work in a heater cycle or a cooler cycle. In a heater cycle, a working fluid expands in the hot chamber, due to heat applied to the chamber, and force is applied to a piston in the chamber by the expanding fluid. The heated fluid is forced from the high temperature chamber to the low temperature chamber through the regenerator, which absorbs portions of the heat contained in the working fluid. The cooled fluid, which can be further cooled in a heat exchanger, is returned to the high temperature chamber through the regenerator. The cooled fluid absorbs heat from the regenerator. The working fluid is then reheated to repeat the cycle.
A multi-cylinder Stirling engine (MSE) is described in U.S. Pat. No. 4,392,351. The MSE includes a bi-directional regenerator and a Stirling engine as described in U.S. Pat. No. 3,985,110. Unfortunately, the MSE uses a reciprocating movement of the rotors, which requires a complex mechanism and results in lower efficiency than a continuous movement. Also, the complex mechanical mechanisms require significant maintenance and sealing of the chambers is difficult due to the rotating plates used, which result in additional dynamic sealing surfaces. Further, the MSE uses a complex and torturous flow path for the fluid which decreases efficiency and increases compression of the fluid in the regenerator. Also, the regenerator for the MSE is external to the Stirling engine, requiring extra space, piping, and fittings.
The MSE also uses a pair of fixed and movable plates to control the phasing of the thermodynamic cycles. Unfortunately, these plates add to the size, weight, complexity, and cost of the engine. Further, the plates limit the surface area of the low and high temperature chambers that is in contact with the heat and cold sources necessary to motivate the Stirling cycle. For example, the ends of the chambers are essentially blocked by the respective plates. To make up for this loss of heat transfer capability, heat exchangers are used. Unfortunately, the exchangers decrease the efficiency and increase the size, complexity, and cost of the MSE.
The MSE attaches rotor lobes to exterior walls of chambers and rotates the chambers to affect movement of the attached rotors. Unfortunately, the rotation of the chambers further limits the direct exposure of the chambers to the cold and heat sources needed to power the Stirling cycle and can lead to seal problems.
A rotary Stirling engine (RSE) is described in U.S. Pat. No. 5,335,497. The efficiency of a heat engine is directly related to the change in pressure for the working fluid during the thermodynamic cycle. Unfortunately, the RSE does not isolate the hot and cold chambers. Thus, the compression of the working fluid occurs in the heat exchangers as well as the chambers, which decreases the efficiency of the engine. Also, the heat transfer between the working fluid and the heat exchangers is limited, since the working fluid is not allowed to remain at rest in the exchangers during the cycles. Further, the external heat exchangers and associated piping add to the size, complexity, and cost of the engine. Also, no more than two volumes can be created in each chamber, limiting the number of thermodynamic cycles that can be completed by one revolution of the rotors in the chambers. In addition, the RSE includes a complex flow path for the working fluid that results in reduced efficiency.
A rotary engine (RE) using separate compressor and combustion chambers is described in U.S. Pat. No. 4,901,694. Each chamber includes a single rotor with two lobes. Unfortunately, using only one rotor per chamber limits the number of cycles that can be completed per rotation of the rotors. Further, the RE uses valves incorporated in the rotors themselves, adding significantly to the complexity and cost of the RE. The gear train for the RE also is complex. For example, to move each rotor through one cycle per rotation, a sequence of four elliptical gears is used. Further, the gear train is one-sided, which results in vibration problems. The complex system of the RE requires extensive maintenance and is difficult to seal.
U.S. Pat. No. 6,996,983 (Cameron) teaches the general concept of a heat exchanger in use with a regenerator in a Stirling engine (heat sinks 126 and 130 and regenerator 130). Unfortunately, Cameron's teachings are limited to an engine with a linear motor and sliding displacer and are inapplicable to systems with rotary motors and rotating compression/expansion configurations.
U.S. Pat. No. 6,865,887 (Yamamoto) teaches the use of position sensing in a Sterling engine. Unfortunately, Yamamoto does not sense operational parameters such as temperature and pressure and therefore, is of no use in providing information about operating conditions in the engine. Further, Yamamoto's teachings are limited to an engine with a linear motor and sliding displacer and are inapplicable to systems with rotary motors and rotating compression/expansion configurations.
U.S. Pat. No. 6,701,708 (Gross et al.) teaches the use of an electric motor to rotate vanes in a Stirling engine. Further, Gross teaches an extremely unusual arrangement which is non-analogous to systems with rotary motors and rotating compression/expansion configurations.
U.S. Pat. No. 5,907,201 (Hiterer et al.) teaches a synchronous linear electric motor linked to drive a displacer in a displacer assembly for a Stirling cycle system. Cameron's teachings are inapplicable to systems with rotary motors and rotating compression/expansion configurations.
U.S. Pat. No. 4,389,849 (Gasser et al.) teaches the use of linear motors (48 and 52) to drive a piston and displacer. However, these teachings are inapplicable to systems with 30 rotary motors and rotating compression/expansion configurations. Gasser also teaches the use of position sensors and feedback for the control of a Sterling cycle cooler. Unfortunately, Gasser does not sense operational parameters such as temperature and pressure and therefore, is of no use in providing information about operating conditions in the engine.
U.S. Pat. No. 4,103,491 (Ishizaki) teaches heat exchanger (29) in-line between regenerator (23) and working chamber (6). However, Ishizaki teaches an unusual lobe configuration which is non-analogous to a system with rotors.
U.S. Published Application No. 2003/0215345 (Holtzapple et al.) teaches the use of proximity sensors and feedback for the control of oil temperature to regulate a gap in a gerotor apparatus for a Brayton cycle engine (see FIGS. 10-15 and page 5). Holtzapple also teaches the use of a flow measuring device to control air flow to a gap in the apparatus (see FIG. 7 and page 4). Unfortunately, Gasser does not sense operational parameters such as temperature and pressure associated with compression and expansion chambers and therefore, is of no use in providing information about operating conditions in the chambers.
What is needed is a thermodynamic cycle heat engine with isolated compression, transfer, and expansion cycles and optimized regeneration of the working fluid. Further, a means for increasing the number of thermodynamic cycles associated with each revolution of rotors in the chambers and an efficient gear train for controlling the rotors and cycles are needed. Also, it would be desirable to reduce the complexity of the engine and enable a greater exposure of the high temperature chamber and low temperature chambers to the respective thermal sources. What is further needed is improvement of the efficiency of the connection between motors and the rotors, sensing of parameters associated with operation of the chambers, additional heat exchange capability, and a simplified flow path and structure.